The present invention relates generally to electronic assemblies and more particularly to butt joined electronic assemblies and modules operating at millimeter wavelength frequencies.
Recent advancements in optical communications technology have demonstrated optical data demuxing at a speed of over 160 Gbit/sec through a single mode optical fiber. At the same time, there is a lack of corresponding progress in test and measurement instrumentation to support analyzing these fast optical pulses. Current solutions are limited by interconnect issues that limit bandwidth and signal integrity, and manufacturing issues that can substantially increase the cost of components. One commercial solution is to couple an enclosed photodetector module with a conventional enclosed sampling head using a coaxial transmission line. The coupled modules are mounted in an optical plug-in module for a sampling oscilloscope. Another solution is to buy a high-speed photodetector as the optical-to-electrical (O/E) converter and use a sampling oscilloscope to capture the signal. This approach seems more beneficial for users because, in addition to having to spend less money, they can also maintain the electrical input to the scope for other testing needs. The inconvenience to users is that the screen is no longer calibrated for accurate power measurements. However, this inconvenience can be overcome by purchasing a separate power meter and perform a calibration manually. Users are faced with the choice of spending more money for the added power level calibration feature of an optical plug-in module or save $10 to 15 thousand dollars by buying a photodetector separately such that both electrical inputs and optical inputs can be measured with the same investment. The latter choice also provides users with a power meter which can be used elsewhere as well.
A common weakness for the above two solutions is that they both need electrical interconnections to connect the photodetector output to the sampler input. Because of the high frequencies involved, the connectors are quite expensive. Moreover, aside from introducing additional costs to the system, these components also introduce unwanted impedance mismatching that produces in signal reflections. These signal reflections result in waveform distortion as a function of bit pattern when measuring fast repetitive signals, such as the RZ 40 Gb/Sec optical data.
A solution to these problems is to combine the detector and sampler semiconductor devices together to form a fully integrated photodetector-sampler IC design. This would eliminate all of the interconnecting hardware between the photodiode and sampler. While a fully integrated photodetector-sampler design (FIPS) sounds good, it runs into practical problems during implementation. Generally, test equipment manufactures are not vertically integrated companies that have the processing technology or the equipment to produce FIPS designs. In addition, high speed photodetector manufacturers generally specialize in producing optical components, such as O/E and E/O converters, but not electrical components, such as electrical samplers. Conversely, electrical component manufactures do not manufacture optical components. To produce the FIPS design would require capital investment and technology development by optical or electrical component manufactures or the test and measurement equipment manufacturer.
Another issue with the FIPS design is yield loss of the final assembly if either of the optical detector or sampler sections develop problems. The photodiode performance cannot be accurately characterized until permanently mounted on or within a carrier or housing, an optical fiber aligned to the photodiode, and electrically coupled to the sampler section. If the output of the competed FIPS device does not meet design specifications, it is difficult to determine if the problem has to do with the fiber alignment, photonic and impulse responses of the diode, polarization sensitivity and the like in the optical detector section or signal gain, sensitivity and the like in the sampler section. Even if the performance problem can be identified to one of the sections, replacing the defective section may lead to damage of the other section.
Another problem with the FIPS design is negotiating refunds on defective parts. Since different manufacturers make the components for the optical and sampler sections and one or the other or a system integrator, such as the test and measurement manufacturer, performs the final integration, determining the cause of the failed part or parts in the sections can be a source of conflict. For example, the problem may be determined within the photodetector module, say a lower than spec photo response. The problem could have been caused by the photodiode die being damaged during the FIPS processing; the optical fiber being misaligned from the integrator assembly process; the optical fiber end surface polishing being flawed; the fiber/detector IC junction having foreign contaminations not readily visible to the eye; the wire bond from the detector IC to the sampler IC having excessive inductance introduced by improper wirebonding; the wirebonder damaging the detector IC by improper bonding control, such as excess bond head ultrasonic energy or pressure, and the like. The photodetector IC manufacturer may be reluctant to refund the cost of the multi-thousand dollars detector IC where the defect is caused by a defective assembly process.
What is needed is an electronic assembly and module design that overcomes the shortcomings of the FIPS and the coaxial interconnect designs. The electronic assembly and module design should allow independent testing and verification of separate sections of the module prior to final assembly or integration. The electronic assembly and module should allow for easy assembly and alignment of the separate device sections down to the micron level.
Accordingly, the present invention is to a butt joined opto-electronic assembly and module for millimeter wavelength frequencies that allows independent alignment of coplanar transmission structures formed on opto-electrical and electrical elements in a proximate abutting relationship. The opto-electrical and electrical elements are mounted on respective independently positioned and mechanically joined open end face carriers and housings. The butt joined opto-electronic assembly has first and second carriers with each carrier having an open end face. The first carrier has an opto-electrical element positioned on the carrier. The opto-electrical element has an opto-electrical device formed on at least a first horizontal surface of the carrier that is coupled to receive an optical signal from an optical waveguide secured to the carrier. The second carrier has an electrical element positioned on the carrier with an electrical device formed on at least a first horizontal surface of the electrical element.
The opto-electronic module has first and second housings with each housing having sidewalls and end walls. A cavity is formed in the housing bounded on three sides by the sidewalls and one of the end walls. Each cavity intersects the other end wall of its housing defining an open end face on the housing. The first housing has the opto-electrical element positioned in the cavity of the housing. The opto-electrical device formed on the horizontal surface of the opto-electrical element is coupled to receive an optical signal from an optical waveguide secured to the first housing. The second housing has the electrical element positioned in the cavity of the housing with the electrical device formed on the horizontal surface of the electrical element. Each housing may be provided with a removable top cover that is mounted on the end wall and the sidewalls bounding the cavity. Preferably, a single removable top cover is mounted on the end walls and the sidewalls bounding the cavities of the first and second housings.
Each of the opto-electrical and electrical elements has a coplanar transmission structure formed on one of the horizontal surfaces. Each coplanar transmission structure is electrically coupled to one of the respective opto-electrical and electrical devices. A standoff dielectric substrate is positioned in an abutting relationship with at least one of the opto-electrical and electrical elements. The standoff dielectric substrate has opposing vertical walls and a horizontal surface on which is formed a coplanar transmission structure. The coplanar transmission structure on the standoff dielectric substrate extends to two of the opposing end walls of the substrate and is positioned in a coplanar relationship with the abutting opto-electric or electrical element and electrically couple via substantially flat electrical conductors. The coplanar transmission structures of the standoff dielectric substrate and the other of the opto-electrical and electrical elements are independently aligned in three mutually perpendicular planes and positioned in a proximate abutting relationship. The first and second carriers of the opto-electronic assembly and the first and second housings of the opto-electronic module are independently positioned and mechanically joined together as a single assembly or module at the open end faces by a securing member with the first and second carriers or modules being linearly and rotationally positionable in three mutually perpendicular planes relative to each other to align the coplanar transmission structures of the standoff dielectric substrate and the other element of the opto-electrical and electrical elements. Substantially flat electrical conductors, such as wedge bonded electrical conductors, electrically couple the coplanar transmission structures of the standoff dielectric substrate and the other element of the opto-electrical and electrical elements together. The invention may also be implemented with a standoff dielectric substrate abutting each of the opto-electrical and electrical elements with the coplanar transmission structures of the standoff dielectric substrates being independently aligned in three mutually perpendicular planes and in a proximate abutting relationship.
In the preferred embodiment, the securing member has removable mechanical attachment members secured to the side surfaces of the first and second carriers or modules. The removable attachment members are secured on the side surfaces of the first and second carriers or modules adjacent to their respective open end faces. Each removable attachment member has first and second links secured to the respective side surfaces of the carriers and housings with each link having a base and at least a first extension member. At lest one of the extension members of each of the first and second removable attachment members projects past one of the open end faces to overlap the other extension member. The overlapping extension members are secured together to join the carriers or housings together as a single assembly or module. In the preferred embodiment, solder is applied to the overlapping extension members. Alternately, an adhesive, such as an epoxy or ultraviolet cured epoxy, may be applied to the overlapping extension members.
The standoff dielectric substrate and the abutting one of the opto-electrical and electrical elements and the other of the opto-electrical and electrical elements may be positioned on the carriers of the assembly and in the cavities of the opto-electronic module housings away from the open end faces of the carrier and housings. One or both of the standoff dielectric substrate and the other of the opto-electrical and electrical elements may also extend to the open end faces of the carriers or housings or one or both may extend past the open end faces of the carriers or housings. Each of the standoff dielectric substrate and associated element and the other of the elements may be positioned on their respective carrier or housing in any of the above positioning relationships so long as the proximate abutting relationship of the coplanar transmission structures of the standoff dielectric substrate or substrates and the other of the elements produces a sub-millimeter separation between the ends of the coplanar transmission structures. For example, the standoff dielectric substrate abutting the opto-electrical element may be set back from the end face of its carrier or housing and the electrical element may extend past the open end face of its carrier or housing.
A mounting dielectric substrate may be mounted on one or both of the carriers of the opto-electronic assembly or in one or both of the cavities of the opto-electronic module housings. Each substrate has an end face that may be positioned away from the open end face of its carrier or housing, extend to the open end face of the carrier or housing, or extend past the open end face of the carrier or housing. The standoff dielectric substrate or substrates and the opto-electrical and electrical elements are secured to the mounting dielectric substrates with the standoff dielectric substrate or substrates and the other of the opto-electrical and electrical elements positionable away from, extending to or extending past the end face of its mounting dielectric substrate. Multiple positioning combinations of the mounting dielectric substrate or substrates may be combined with the multiple positioning combinations of the standoff dielectric substrate or substrates and the other of the opto-electrical and electrical elements. For example, the opto-electrical section or module may have the mounting dielectric substrate positioned away from the open end face of the carrier or housing with the standoff dielectric substrate abutting the opto-electrical element extending past the end face of the mounting dielectric substrate. The electrical section or module may have the electrical element positioned on the carrier or in the cavity of the housing with the electrical element extending past the open end face of the carrier or housing. In another example, the opto-electrical and electrical sections or modules may each have a mounting dielectric substrate mounted on the respective carriers or in the respective cavities of the housings. The mounting dielectric substrates may both extend past the open end faces of their respective carriers or housings with each of the opto-electrical and electrical elements having abutting standoff dielectric substrates that extend past the end faces of their respective mounting dielectric substrates.
The opto-electrical device formed on the opto-electrical element may be an optical-to-electrical converter, such as a photodiode, a semiconductor laser, an optical modulator or other types of devices that receives an electrical signal to generate or modulate an optical device or generates an electrical signal in response to a received optical signal. The electrical device formed on the electrical element may be at least a first sampling diode of a sampling circuit, a laser driver, an amplifier or the like.
The objects, advantages and novel features of the present invention are apparent from the following detailed description when read in conjunction with appended claims and attached drawings.